This invention relates to processes used in the conditioning of fuel oils to provide for a cleaner burning and more thermally efficient fuel.
Fuel oils contain suspended particles of matter called asphaltenes which are high molecular weight residues of the petroleum distillation process. The presence of asphaltenes in a fuel oil creates problems in both the storage and burning of the fuel. The high molecular weight of this residue causes it to settle at the bottom of storage tanks, forming a solid mass thus necessitating frequent and costly cleaning. Moreover, these relatively insoluble particles tend to clog oil strainers and filters, and will eventually foul the oil heater and burner tip resulting in frequent repairs and corresponding high maintenance costs.
When fuel oils containing a substantial asphaltene content (e.g. 2-12 weight%) are burned a variety of problems result. As the asphaltene is more difficult to burn a significant amount of this material passes through the furnace as unburned particulate matter thus causing a substantial decrease in the thermal efficiently of the fuel.
The unburned particulate matter also creates serious environmental problems. The unburned combustibles which pass through the furnace are frequently low density, electrically conductive cenospheric materials having a high carbon content. Such physical properties render the non-combusted matter incapable of being efficiently collected by electrostatic precipitators thereby causing an increase in particulate emissions. To compound the environmental problem, the unburned carbon tends to absorb sulfuric acid, a by-product of the combustion of high sulfur oils, in the combustion system and stack, resulting in acid smut fallout.
Various treatments of very heavy hydrocarbon fuels to prepare them for further processing are disclosed in U.S. Pat. Nos. 1,390,231, 1,618,669 and 1,770,181. Generally, these disclosures teach methods for homogenizing heavy fuel mixtures containing liquid hydrocarbon and coarse pitch-forming, coke-like particles of solid impurities. U.S. Pat. No. 1,618,669 describes a method whereby the fuel is separated into its solid and liquid components. Likewise, U.S. Pat. Nos. 1,390,231 and 1,770,181 teach homogenizing the oil using mechanical work to disperse and decrease the size of coarse ashes and coke-like particles.
None of this early work is directed to mitigating the effects of small, but bothersome concentrations of asphaltenes in heavy fuel oils (e.g. fuel oil numbers 4-6) resulting in the problems associated with acid smut fallout.